The winger was initially drafted to Stirling County, but with their matches now finished County agreed that Ayr could take him for their final match at Hawick if both clubs agreed.
Peter Laverie, the Ayr coach, told the Scotsman: “Hawick were happy with that. The game is not crucial to league positions now and we have injuries in our back division and our reserve team have a league match this weekend too.
“We will wait and see whether Robbie Fergusson is fit to play before we make a decision on whether Carlin starts or not, but he’s a nice lad and we’ll be happy to give him his introduction to Scottish rugby.”